Photographic process for forming a positive color image utilizing a photochromic composition containing a spiropyran compound, a photoactivator and poly-n-vinyl- carbazole

ABSTRACT

A photographic process in which a positive colour image is produced by the steps of: PROVIDING A RECORDING MATERIAL WHICH COMPRISES IN INTIMATE ADMIXTURE: 1. AT LEAST ONE SPIROPYRAN COMPOUND, 2. AT LEAST ONE ORGANIC POLYHALOGEN COMPOUND SENSITIVE TO ULTRAVIOLET RADIATION AND CAPABLE OF PRODUCING ON EXPOSURE WITH ULTRAVIOLET RADIATION WITH THE SPIROPYRAN COMPOUND A DYE SALT AND IN WORKING RELATIONSHIP WITH SAID MIXTURE A COMPOUND CONTAINING N-vinylcarbazole units, IMAGE-WISE EXPOSING THE RECORDING MATERIAL TO ACTIVATING ELECTROMAGNETIC RADIATION TO SUCH A DEGREE THAT A LATENT DYE IMAGE OR FAINTLY COLOURED VISIBLE DYE IMAGE IS OBTAINED, OVERALL HEATING THE IMAGE-WISE EXPOSED RECORDING MATERIAL TO SUCH A DEGREE THAT BY A SUBSEQUENT OVERALL EXPOSURE OF THE HEATED RECORDING MATERIAL WITH INFRARED RADIATION OPTIONALLY MIXED WITH WHITE LIGHT A POSITIVE COLOUR IMAGE IS FORMED, AND OVERALL EXPOSING THE THUS OVERALL HEATED RECORDING MATERIAL WITH INFRARED RADIATION OPTIONALLY MIXED WITH WHITE LIGHT PRODUCING THEREBY A POSITIVE COLOUR IMAGE.

United States Patent [191 Van Royen et al.

[4 1 Nov. 12, 1974 1 PHOTOGRAPHIC PROCESS FOR FORMING A POSITIVE COLOR IMAGE UTILIZING A PHOTOCHROMIC COMPOSITION CONTAINING A SPIROPYRAN COMPOUND, A PI-IOTOACTIVATOR AND POLY-N-VINYL- CARBAZOLE [75] Inventors: Freddy Ghisleen Van Royen,

Wommelgem; Jozef Willy Van Den Houte, Berchem, both of Belgium [73] Assignee: AGFA-Gevaert, Mortsel, Belgium [22] Filed: Feb. 21, 1973 [21] Appl. No.: 334,246

[30] Foreign Application Priority Data June 26, 1972 Great Britain 29917/72 [52] US. Cl. 96/48 R, 96/90 PC, 96/90 R [51] Int. Cl G036 5/24, G036 H52 [58] Field of Search 96/48 R, 48 HD, 90 PC, 96/90 R [56] References Cited UNITED STATES PATENTS 3,607,266 9/1971 Yamada et al 96/48 R 3,697,276 10/1972 Lewis et a1 96/90 R FOREIGN PATENTS OR APPLICATIONS 1,274,655 8/1968 Germany 96/90 PC Primary ExaminerDavid Klein Assistant Examiner-Won H. Louie, Jr. Attorney, Agent, or FirmWilliam J. Daniel [57] ABSTRACT A photographic process in which a positive colour image is produced by the steps of:

providing a recording material which comprises in intimate admixture:

l. at least one spiropyran compound,

2. at least one organic polyhalogen compound sensitive to ultraviolet radiation and capable of producing on exposure with ultraviolet radiation with the spiropyran compound a dye salt and in working relationship with said mixture a compound containing N-vinylcarbazole units,

image-wise exposing the recording material to activating electromagnetic radiation to such a degree that a latent dye image or faintly coloured visible dye image is obtained,

overall heating the image-wise exposed recording material to such a degree that by a subsequent overall exposure of the heated recording material with infrared radiation optionally mixed with white light a positive colour image is formed, and

overall exposing the thus overall heated recording material with infrared radiation optionally mixed with white light producing thereby a positive colour image.

13 Claims, N0 Drawings PHOTOGRAPHIC PROCESS FOR FORMING A POSITIVE COLOR IMAGE UTILIZING A PHOTOCHROMIC COMPOSITION CONTAINING A SPIROPYRAN COMPOUND, A PHOTOACTIVATOR AND POLY-N-VINYL- CARBAZOLE This invention relates to the production of positive colour images with recording materials containing a mixture of a photosensitive polyhalogen compound and a dye precursor compound and to recording materials containing such mxiture.

Non-silver free-radical photography by means of recording materials containing a mixture of a photosensitive polyhalogen compound such as carbon tetrabromide and a dye precursor compound such as leuco crystal violet have been described already in the United Kingdom Pat. Specification No. 1,180,883.

These recording materials are suited for the production of print-out colour images i.e. colour images having reversed image values with respect to the original.

It is an object of the present invention to provide a photographic colour-forming process of the freeradical type resulting in the production of positive colour images i.e. images having the same image values as the original.

The process of the present invention includes the steps of:

providing a recording material, which comprises in intimate admixture:

l. at least one spiropyran compound,

2. at least one organic polyhalogen compound sensitive to uiltraviolet radiation and capable of producing on exposure with ultraviolet radiation with the spiropyran compound a dye salt and in working relationship with said mixture a compound contain ing N-vinylcarbazole units,

image-wise exposing the recording material to activating electro-magnetic radiation, preferably U.V. radiation, to such a degree that a latent dye image or faintly coloured visible dye image is obtained,

overall heating the image-wise exposed recording material to such a degree that by a subsequent overall exposure of the heated recording material with infrared radiation optionally mixed with white light a positive colour image is formed, and

overall exposing the thus overall heated recording material with infrared radiation optionally mixed with white light producing thereby a positive colour image.

Preferred spiropyran compounds for use according to the present invention contain at least one pyran ring having in the orthoand meta-positions with respect to the oxygen atom a condensed benzo or naphtho ring or other aromatic polycyclic ring system including these condensed rings or ring systems in substituted state, e.g. an anthraceno or a phenanthreno ring system e.g. as present in a spirodib enzopyran, a spirodinaphthopyran, a spirobenzonaphthopyran, a l ,3,3- trimethylindolinobenzospiropyran, a 1,3,3- trimethylindolinonaphthospiropyran or such spiropyrans containing condensed aromatic nuclei of the anthracene or phenanthrene type.

In said spiropyrans the pyran rings, the condensed benzo, the condensed higher atomatic rings as well as the 1,3,3-trimethylindolino ring may be substituted.

Suitable substituents therefor are, e.g., hydrocarbon groups such as alkyl groups, e.g. lower alkyl groups such as methyl, substituted alkyl groups e. g. substituted with halogen, or phenyl-substituted alkyl groups, alkylene ester groups e.g. a CH COOC H group, alkylene carboxyl groups e.g. a -Cl-l -COOH group, alkylene carbonamide groups or such groups in which the carbonamide group is substituted e.g. a

group, an acyl group e.g. acetyl, halogen, nitro, hydroxy, an alkoxy or aryloxy group or a substituent linking together the carbon atoms in 3,3'-position in the spiropyran system e.g. a (CH ),,-chain wherein n is 2 or 3 General formulae covering particularly suited spiropyrans are the following:

wherein:

each of R, R R',, R R';;, R and R;, represents hydrogen, an aliphatic group including a substituted aliphatic group e.g. a (C -C alkyl group including such an alkyl group in substituted form, e.g. methyl, ethyl, propyl, amyl or hexadecyl, an halogen-substituted alkyl group, an alkylene ester group e.g. CH -COOC H an alkylene carboxyl group e.g. -CI-I COOH, an alkylene carbonamide group or such a group in which the carbonamide group is substituted e.g.

an acyl group, halogen, nitro, hydroxy, an alkoxy or aryloxy group, a phenyl group or a substituted phenyl group, piperidyl, or R and R together represent a (CH chain wherein n 2, the carbon atoms in the 3- and 3'-positions together.

Suited spiropyran compounds and their preparation are described in the published German patent application Nos. 1,274,655 filed Dec. 15, 19 65 by Telefunken or 3 to link TABLE 1 Meltin spiropyran compound point C. (1) 257 (2) Ill-I 204 g o o (3) H: EH-C H3 208 (5) fi/HP OOI'I I 164 (6) (LIE-00002115 166 Q g C C -MWWMHH v ([lHz-CO-NH Q TAB LE 1-C0ntinued Meltln Spiropyran compound point 05 my..." C1 lso CiXiCQ TABLE I Continued Melting point C.)

Spiropyran compound In order to illustrate in more details the preparation of'the spirobi(arylopyran)-compounds and the sprio(indolino, arylopyran)-compounds the following preparation receipts are given:

Preparation 1 Preparation of 3-methyldi-B-naphthospiropyran (compound 2 of Table 1) In a 2 litre three-necked flask, fitted with a reflux condenser and a gas inlet tube reaching nearly the bottom of the flask are introduced;

ethanol 1 litre butanone 22 ml (0.25 mole) 2 hydroxy-l-naphthaldehyde 86 g (0.5 mole) The flask shaken until partial dissolution of the ingredients. Dry hydrogen chloride gas is introduced at a rate, which allows complete absorption and the start of ethanol reflux. Thereupon the already strongly blue coloured mixture is cooled in a mixture of ice and sodium chloride and the introduction of hydrogen chloride gas is continued until saturation. In the reaction mixture green crystals of pyrylium salt form and the crystallization is allowed to proceed overnight in a refrigerator.

The pyrylium salt formed is separated by suction, washed with ethanol and thereupon brought into suspension in 300 m1 of ethanol.

Whilst stirring, a percent by weight aqueous solution of ammonium hydroxide is added until the mixture is definitely alkaline. During that operation the mixture turns colourless.

The obtained crystalline product is separated by suction, washed with water and dried.

Finally the spiropyran compound is recrystallized from 600 ml of benzene and again separated and dried under reduced pressure at 50-60C.

Yield: 45 g. Melting point: 204C.

PREPARATION 2 Preparation of 1,3,3-trimethylindolinobenzopyrylospiran (compound 22 of Table 1) In a 100 ml flask fitted with a reflux condenser are introduced the following ingredients:

salicylaldehyde 3.7 g (0.03 mole) 1,3,3-trimethyl-2-methylene 5.1 g (0.03 mole) indolenine ethanol 90 ml The solution is refluxed for 2 h whereupon it is cooled and filtered.

To the filtrate water is added for separation of a solid product. The, solid is separated by suction, washed with water and dried under vacuum conditions.

The spiran compound is recrystallized from ml of hexane.

Yield: 5 g. Melting point: 9394C.

It is assumed that during the photoexposure a dyestuff salt having the pyrylium structure forms when a spirobi(arylopyran) compound is used and a dyestuff salt having the indolinium salt structure forms when a spiro(indolino-arylopyran) compound is used.

Suited organic polyhalogen compounds sensitive to ultraviolet radiation and capable of photolytically separating a halogen-containing free radical and of forming a dye salt with the spiropyran compound are within the scope of the following general formula:

wherein:

each of A, B, X and Y is a halogen atom of the group of chlorine, bromine or iodine, or

wherein one of said symbols A, B, X or Y represents an alkyl group, including a substituted alkyl group e.g. a halogen-substituted alkyl group, a hydroxyalkyl group or an aralkyl group e.g. benzyl, an aryl group, a substituted aryl group or an aroyl group, and the other symbols chlorine, bromine or iodine, or wherein at least two of said symbols A, B, X or Y represent an aromatic acyl group, e.g. benzoyl, and the other symbols chlorine, bromine or iodine.

Suitable representatives falling within the scope of that general formula are organic halides such as carbon tetrabromide, bromoform, iodoform, hexachloroethane, hexabromoethane, pentabromoethane, 1,1 ,2,2- tetrabromoethane, 04,0:,a-tribromoacetophenone and tribromoethanol.

The colour-forming spiropyran compound(s) are preferably used in admixture with a 1- to 20-fold amount by weight of photosensitive organic polyhalogen compound such as carbon tetrabromide.

This ratio, however, is not limitative since useful results can be obtained with the colour-forming compound and photosensitive polyhalogen compound in a ratio by weight in the range of e.g. 1:1 to 1:50.

The recording material for forming a positive dye image according to the present invention is characterized by the presence in the recording layer of a compound containing N-vinylcarbazole units.

Preferably a N-vinylcarbazole homopolymer or copolymer is used in an amount large enough to serve as binder for the spiropyran compound and the organic polyhalogen compound sensitive to ultraviolet radiation.

Suitable N-vinylpolymers and copolymers can be prepared by application of one of the various known polymerization procedures, e.g., by pearlor emulsion polymerization or by polymerization in solution, whereby the initiation of the polymerization can occur by free radicals, by ion formation, or by radiation, e.g., with actinic light. It is to be noted that the polymerization degree is not critical and can vary between wide limits. As far as the copolymers are concerned it is further to be noted that the content of N-vinylcarbazole units can vary between wide limits, say, e.g. between 20 and 95 In general, the best results are attained with copolymers having a content of vinylcarbazole units between 40 and The preparation of suitable poly-N-vinylcarbazoles is described, e.g., in the German Pat. Specification Nos.

931,731 filed Mar. 4, 1953; 936,421 filed Feb. 20, 1953; 1,097,680 filed Oct. 15, 1959 all three by Badische Anilin- & Soda-Fabriken A.G., and 1,158,367 filed July 18, 1962 by Gevaert Photo-Production NV. and

the US. Pat. No. 2,072,465 of W. Reppe, E. Keyssner and E. Dorrer, issued Mar. 2, 1937.

Table 2 Copolymer mole of N-vinyl carbazole copolymer of N-vinylcarbazole and vinylidene chloride 85.4 copolymer of N-vinylcarbazole and 3,3',5-trimethyl 93 isononyl ether copolymer of N-vinylcarbazole and vinyl acetate 88.6 copolymer of N-vinylcarbazole and isopropenyl acetate 94.5 copolymer of N-vinylcarbazole and vinylstearate 37.5 copolymer of N-vinylcarbazole and methyl acrylate 67.6 copolymer of N-vinylcarbazole and ethyl acrylate 41 graft copolymer of N-vinylcarbazole and ethyl acrylate 90.3 emulsion polymer of N-vinylcarbazole and polyethyl 94.5 acrylate copolymer of N-vinylcarbazole and n-butyl acrylate 58.3 copolymer of N-vinylcarbazole and 2-ethyl hexyl 51.6 acrylate copolymer of N-vinylcarbazole and 76.6 acryloxyethyldiethylamine copolymer of N-vinylcarbazole and vinylcinnamate 92.5 copolymer of N-vinylcarbazole and methyl 62.7 methacrylate copolymer of N-vinylcarbazole and isobutyl 51.8 methacrylate copolymer of N-vinylcarbazole and lauryl methacrylate 77.4 copolymer of N-vinylcarbazole and 9.7 methylacryloxyethyldiethylamine copolymer of N-vinylcarbazole and acrylonitrile 88 graft copolymer of N-vinylcarbazole and butylaldehyde 30 acetal of polyvinyl alcohol copolymer of N-vinylcarbazole and 82.4 di(2-dichloroethyl)-vinylphosphonate copolymer of N-vinylcarbazole and styrene 49 graft copolymer of N-vinylcarbazole and polystyrene 27.3 copolymer of N-vinylcarbazole and vinylnaphthalene 47.1 copolymer of N-vinylcarbazole and anthracene-(9,l) 91.5 copolymer of N-vinylcarbazole and 2-vinylpyridine 31.8 copolymer of N-vinylcarbazole and 4-vinylpyridine 32.4 copolymer of N-vinylcarbazole and N-vinylpyrrolidine 69.1 terpolymer of N-vinylcarbazole, acrylonitrile and 20 styrene graft polymer of a terpolymer of vinyl chloride, vinyl 29.4 acetate, and vinyl alcohol with N-vinylcarbazole graft polymer of a terpolymer of vinyl chloride, vinyl 55.1

acetate, and maleic anhydride with N-vinylcarbazole The recording material of the present invention preferably contains the photosensitive polyhalogen compound and spiropyran compound in a layer whose binder is solely poly-N-vinylcarbazole. However, minor amounts of other binding agents are not excluded and so recording layers of the present invention may contain also hydrophobic polymers and copolymers e.g. on the basis of styrene, vinyl acetate, acrylonitrile, acrylic acid ester, methacrylic acid ester or butadiene units, hydrophobic cellulose derivatives, phenoxy resins or polycondensates of the polyester type, e. g. polycarbonates.

The recording layers of the present invention can obtain an improved sensitivity to ultraviolet radiation and/or visible light by incorporating therein the sensitizing agents described in the United Kingdom patent 1 16 application No. 41,749/ corresponding with published Dutch patent application No. 71/12021.

Particular useful sensitizing agents are organic compounds containing a carbonyl group linked through a conjugated system to a dialkylamino group, e.g. Michlers ketone and 1-methyl-3-phenyl-7-dimethylamino-2( 1H )-quinolone.

A particularly good sensitivity to visible light is obtained with merocyanine dyes, the following dye being an example thereof:

The recording materials of the present invention preferably contain a fog-inhibiting compound such as triphenylstibine and/or analogous compounds described for that purpose in the published Dutch patent application No. 71 12021.

The fog-inhibiting compound is present in the recording layer preferably in a weight ratio range of 1:1 to 1:10 with respect to the spiropyran compound.

The amount of spiropyran compound in the recording layer amounts preferably to at least 0.05 g per sq. m.

The recording composition of the present invention can be coated on any kind of support on which colour images have to be produced. Preferred supports are paper and resin sheets, e.g. those known in silver halide photography. The thickness of the recording layer may vary within relatively broad limits. Dry coatings have preferably a thickness in the range of 3 to 20 microns.

In order to produce a positive colour image according to the present invention the above described recording material in a first step is image-wise exposed to ultraviolet radiation and/or to visible light.

In the step following the formation of the latent or only faintly coloured visible dye image the recording material is heated preferably in the range of to C for a period of time of 5 to 20 sec. This heating may proceed, e.g., with hot rollers or in a drying stove with a hot air stream.

Thereupon an overall exposure with infrared radiation optionally mixed with visible light produces a colouration in the areas of the recording material that not had been exposed image-wise previously.

During the overall infrared exposure overall heating may be continued but preferably at a lower degree, e.g. at 100C.

The stabilization of the obtained positive prints may proceed by washing out the residual photosensitive organic polyhalogen compound e.g. carbon tetrabromide with a suitable solvent or solvent mixture, e.g. a hydrocarbon liquid such as petroleum ether optionally mixed with acetone, or by simply evaporating it by raising the temperature if the compound involved is sufficiently volatile.

According to a special embodiment the stabilization of the image proceeds with increased speed by first overall heating the recording layer at about 80C in the absence of visible light for at least 5 sec. and then treating it with a chlorinated solvent, e.g. perchloroethylene at room temperature (20C) for at least 1.5 sec. in order to extract the photosensitive polyhalogen compound.

Stabilization may proceed very fast by dipping the exposed recording material in a heated organic liquid that has a relatively high boiling point, preferably above 200C and that does not affect the recording layer. The organic liquid is preferably heated in the range of 145 to 165C and the dipping time is, e.g., to 20 sec. Suitable liquids are mineral oil of aliphatic or naphthenic nature, e.g. motor oil, and ISOPAR G (trade name). A post-treatment with a solvent, eg a chlorinated hydrocarbon solvent may be necessary to remove the residual oil film.

The following examples further illustrate the present invention. The percentages are by weight unless otherwise indicated.

EXAMPLE 1 A photosensitive material was prepared by coating the following composition:

0.5 g of carbon tetrabromide 0.04 g of di-B-naphthospiropyran 0.5 g of poly-N-vinylcarbazole 0.02 g of triphenylstibine ml of methylene chloride, at a wet coating thickness of 0.12 mm to a non-subbe polyethylene terephthalate support.

The dried coating was image-wise contact-exposed through a line original and a grey filter of spectral density 1.00. The exposure lasting 8 sec. was effected in an ACTINA S (trade name) diazotype copying apparatus operating with an ultraviolet lamp of 1000 W. A faintly visible print-out image was obtained.

The exposed recording material was then overall heated for 30 sec. at 150C.

Thereupon the heated material was overall exposed with infrared radiation while being in contact with a metal plate at a temperature of about 100C.

The faintly visible print-out image disappeared and an intense blue colouration took place in the areas that had not been exposed image-wise.

The obtained positive image was stabilized by dipping the recording layer for 2 min. in perchloroethylene.

EXAMPLE 2 A photosensitive material was prepared by coating the following composition:

0.120 g of carbon tetrabromide 0.120 g of iodoform 0.120 g of 3-methyl-di-[3-naphthospiropyran 0.020 g of triphenylstibine 0.500 g of poly-N-vinylcarbazole 10 ml of methylene chloride at a wet coating thickness of 0.12 mm to a non-subbed polyethylene terephthalate support.

The iamge-wise exposure and processing including stabilization were carried out as described in Example 1 with the difference, however, that the overall heating at 150C lasted from to 45 sec and the duration of the infrared exposure was from 5 sec. to 1 minute.

EXAMPLE 3 A photosensitive material was prepared and exposed image-wise as described in Example 2. In the processing the overall heating proceeded at 120C for a period of 30 to 75 sec. The other steps of the processing and stabilization were the same as in Example 1. A positive dye image of good quality was obtained.

EXAMPLE 4 A photosensitive material was prepared as described in Example 2.

The image-wise contact exposure proceeded with visible light by means of an incandescent lamp of 300 W placed at a distance of 10 cm.

The overall heating proceeded for 15 sec. at 150C.

The other steps of the processing and stabilization were the same as described in Example 1.

A positive dye image of good quality was obtained.

We claim:

1. A photographic process for producing a positive color image in a recording material which comprises in intimate admixture:

l. at least one spiropyran compound which is a spirobenzopyran, a spirodinaphthopyran, a spirobenzonaphthopyran, a l,3,3-trimethylindolinobenzospiropyran, a l,3,3-trimethylindolinonaphtospiran or a spiropyran containing a condensed anthracene or phenanthrene nucleus; and

2. at least one organic polyhalogen compound that is sensitive to ultraviolet radiation and corresponds to the general formula:

in which:

each of A, B, X and Y is a chlorine, bromine or iodine atom, or

one of A, B, X or Y represents an alkyl group, an aryl group, or an aroyl group, and the remainder chlorine, bromine or iodine, or at least two of A, B, X or Y represent an aromatic acyl group, and the remainder chlorine, bromine or iodine; and

3. within said recording material in working contact with said mixture a polymer of N-vinylcarbazole, which comprises the steps of:

imagewise exposing said recording material to activating electromagnetic radiation to an extent forming a latent dye image or faintly colored visible dye image, overall heating the imagewise exposed recording material to such an extent that upon subsequent overall exposure of the heated recording material to infrared radiation optionally mixed with white light a positive color image is formed, and overall exposing the thus overall heated recording material with infrared radiation optionally mixed with white light producing thereby a positive color image.

2. The process of claim 1 wherein said polymer is of N-vinylcarbazole and up to mol of a different vinyl monomer.

3. A photographic process according to claim 1 wherein said spiropyran compound corresponds to one of the following general formulae:

phenylcarbamyl group, a hydroxy group, an alkoxy group, an aryloxy group, a phenyl group, piperidyl, acetyl, halogen, nitro, or R, and R, together represent a (Cl-l chain wherein n 2 or 3 to link the carbon atoms in the 3 and 3' positions together.

4. A photographic process according to claim 1, wherein the overall heating of the recording material is continued during the overall infrared exposure at a reduced temperature.

5. A photographic process according to claim 1, in which the spiropyran compound and the organic polyhalogen compound that is sensitive to ultraviolet radiation are incorporated into a recording layer containing as binding agent a polymer comprising N- vinylcarbazole units.

6. A photographic process according to claim 5, wherein the binding agent consists of poly-N- vinylcarbazole.

7. A photographic process according to claim 1, wherein the polyhalogen compound is carbon tetrabromide and/or iodoform.

8. A photographic process according to claim 1, wherein the recording material contains triphenylstibine as fog-inhibiting compound.

9. A photographic process according to claim 1, wherein such spiropyran compound is used in admixture with a 1- to 20-fold amount by weight of the organic polyhalogen compound that is sensitive to ultraviolet radiation.

10. A photographic process according to claim 9, wherein as fog-inhibiting compound triphenylstibine is used in a weight ratio range of 1:1 to 1:10 with respect to the spiropyran compound.

11. A photographic process according to claim 1, wherein the image-wise exposure is to ultraviolet radiation and/or visible light.

12. A photographic process according to claim 1, wherein the overall heating is at a temperature in the range of to C for a period of 5 to 20 sec.

13. A photographic process according to claim 12, wherein the overall heating is continued during the overall exposure to infrared radiation but at a temperature below 120C. 

1. A PHOTOGRAPHIC PROCESS FOR PRODUCING A POSITIVE COLOR IMAGE IN A RECORDING MATERIAL WHICH COMPRISES IN INTIMATE ADMIXTURE;
 1. AT LEAST ONE SPIROPYRAN COMPOUND WHICH IS A SPIROBENZOPYRAN, A SPIRODINAPHTHOPYRAN, A SPIROBENZONAPHTHOPYRAN, A 1,3M3-TRIMETHYLINDOLINOBENZOSPIROPYRAN, A 1,3,3TRIMETHYLINDOLINONAPHTOSPIRAN OR A SPUROPYRAN CONTAINING A CONDENSED ANTHRACENE OR PHENANTHRENE NUCLEUS; AND
 2. AT LEAST ONE ORGANIC POLYHALOGEN COMPOUND THAT IS SENSITIVE TO ULTRAVIOLET RADIATION AND CORRESPONDS TO THE GENERAL FORMULA;
 2. at least one organic polyhalogen compound that is sensitive to ultraviolet radiation and corresponds to the general formula:
 2. The process of claim 1 wherein said polymer is of N-vinylcarbazole and up to 80 mol % of a different vinyl monomer.
 3. A photographic process according to claim 1 wherein said spiropyran compound corresponds to one of the following general formulae:
 3. within said recording material in working contact with said mixture a polymer of N-vinylcarbazole, which comprises the steps of: imagewise exposing said recording material to activating electromagnetic radiation to an extent forming a latent dye image or faintly colored visible dye image, overall heating the imagewise exposed recording material to such an extent that upon subsequent overall exposure of the heated recording material to infrared radiation optionally mixed with white light a positive color image is formed, and overall exposing the thus overall heated recording material with infrared radiation optionally mixed with white light producing thereby a positive color image.
 3. WITHIN SAID RECORDING MATERIAL IN WORKING CONTACT WITH SAID MIXTURE A POLYMER OF N-VINYLCARBAZOLE, WHICH COMPRISES THE STEPS OF: IMAGEWISE EXPOSING SAID RECORDING MATERIAL TO ACTIVATING ELECTROMAGNETIC RADIATION TO AN EXTENT FORMING A LATENT DYE IMAGE OR FAINTLY COLORED VISIBLE DYE IMAGE, OVERALL HEATING THE IMAGEWISE EXPOSED RECORDING MATERIAL TO SUCH AN EXTENT THAT UPON SUBSEQUENT OERALL EXPOSURE OF THE HEATED RECORDING MATERIAL TO INFRARED RADIATION OPTIONALLY MIXED WITH WHITE LIGHT A POSITIVE COLOR IMAGE IS FORMED, AND OVERALL EXPOSING THE THUS OVERALL HEATED RECORDING MATERIAL WITH INFRARED RADIATION OPTIONALLY MIXED WITH WHITE LIGHT PRODUCING THEREBY A POSITIVE COLOR IMAGE.
 4. A photographic process according to claim 1, wherein the overall heating of the recording material is continued during the overall infrared exposure at a reduced temperature.
 5. A photographic process according to claim 1, in which the spiropyran compound and the organic polyhalogen compound that is sensitive to ultraviolet radiation are incorporated into a recording layer containing as binding agent a polymer comprising N-vinylcarbazole units.
 6. A photographic process according to claim 5, wherein the binding agent consists of poly-N-vinylcarbazole.
 7. A photographic process according to claim 1, wherein the polyhalogen compound is carbon tetrabromide and/or iodoform.
 8. A photographic process according to claim 1, wherein the recording material contains triphenylstibine as fog-inhibiting compound.
 9. A photographic process according to claim 1, wherein such spiropyran compound is used in admixture with a 1- to 20-fold amount by weight of the organic polyhalogen compound that is sensitive to ultraviolet radiation.
 10. A photographic process according to claim 9, wherein as fog-inhibiting compound triphenylstibine is used in a weight ratio range of 1:1 to 1:10 with respect to the spiropyran compound.
 11. A photographic process according to claim 1, wherein the image-wise exposure is to ultraviolet radiation and/or visible light.
 12. A photographic process according to claim 1, wherein the overall heating is at a temperature in the range of 120* to 150*C for a period of 5 to 20 sec.
 13. A photographic prOcess according to claim 12, wherein the overall heating is continued during the overall exposure to infrared radiation but at a temperature below 120*C. 